The DDI is useful as an antiviral agent and has already been approved as an anti-AIDS drug in many countries including U.S.A., Japan and European countries.
To derive a didehydro (DD) compound from nucleoside, there is conventionally known, for example, a method where hydroxyl groups at the 2′- and 3′-positions of nucleoside are subjected to thiocarbonylation, followed by radical reduction to form a didehydrodideoxy (D4) derivative, and the D4 derivative is subjected to hydrogenation or the like, thereby obtaining a didehydro (DD) derivative (refer to Chu, C. K. et al. J. Org. Chem. 1989, 54, 2217-2225).
Reduction catalysts are used when the didehydro derivative is synthesized from nucleoside. Noble metal-supported catalysts can produce the target compounds in satisfactory yields. However, those catalysts themselves are so expensive that it was difficult to use those catalysts in large amounts.
Accordingly, there is an increasing demand for methods for producing the DDI and DDA in high yields at low cost.